AbstractA number of 15 new solvates containing pyridine‐N‐oxide of the general formula M(C5H5NO)mn+ (anion)n− is reported. In these compounds M = Li, Na, Mg, Ca, Sr, Ba, Mn, Fe, Co, Cu, Zn, Cd, Pb, and Tl, n = 1‐3, m = 3‐8, and the anions are ClO4− and BF4−.The compounds are identified by chemical analysis and by means of physical measurements.The shift towards lower wave numbers in the N‐O stretching frequency of the complexes is discussed. Far‐infrared spectra in the region 700‐200 cm−1 have also been investigated. A correlation between νNO and νMO is reported.Ligand‐field spectra for the transition‐metal solvates of Co(II) and Ni(II) have been re‐investigated. New values for Dq and B are reported, and the ligand is placed in the spectrochemical and nephelauxetic series.The Mössbauer spectrum of Fe(C5H5NO)6(ClO4)2 is discussed. Electron paramagnetic resonance spectra of the solvates of Mn(II), Ni(II), and Cu(II) have been investigated. No static Jahn‐Teller distortion of the species Cu(C5H5NO)62+ is observed at room temperature.Pyridine‐N‐oxide is concluded to be a rather strong ligand, as reflected by the facts that preparation of metal solvates is often possible from the hydrated metal salts without dehydration, and the rather high values of Dq/B calculated from the spectra of the cobalt(II) and nickel(II) solvates.